This invention relates to contact lens hydrogels and, more particularly, to a new and improved hydrogel prepared by ultraviolet initiated copolymerization.
Copolymers of N-vinyl lactams such as N-vinyl pyrrolidone (NVP) and hydrophobic acrylates such as phenylethyl methacrylate (PhEMA) are potentially useful hydrogel materials, for example for soft contact lens applications. The copolymers are particularly appropriate for high water content lenses (70-85% by weight of water) because they are strong materials in spite of their high water content. For example, a copolymer of 83% NVP and 17% PhEMA had a tensile strength of 8.3 kg/cm.sup.2 after hydration to an equilibrium water content of 73 grams of water per 100 grams of dry polymer.
When an attempt is made to prepare lenses from this material by sectioning rods of the copolymer prepared by thermal initiation, the materials have been found to be too soft to machine and polish satisfactorily. Attempts to avoid machining by casting the polymers directly into lens-shaped molds provides stiff leathery unsatisfactory specimens, particularly where the PhEMA concentration is greater than about 15%. If the PhEMA concentration is limited to 15% or less, however, the tensile and tear strength of the hydrogel are unsatisfactory.
Accordingly, it is an object of the present invention to provide new and improved contact lens hydrogels which overcome the above-mentioned disadvantages of the prior art.
Another object of the invention is to provide contact lens hydrogels made from copolymers of N-vinyl lactams and hydrophobic acrylates having improved strength characteristics and physical properties.